A monotonicity result under symmetry and Morse index constraints in the plane

Abstract

This paper deals with solutions of semilinear elliptic equations of the type \[ \left\{\begin{array}{@{}ll} -\Delta u = f(|x|, u) \qquad & \text{ in } \Omega, \\ u= 0 & \text{ on } \partial \Omega, \end{array} \right. \] where Ω is a radially symmetric domain of the plane that can be bounded or unbounded. We consider solutions u that are invariant by rotations of a certain angle θ and which have a bound on their Morse index in spaces of functions invariant by these rotations. We can prove that or u is radial, or, else, there exists a direction $e\in \mathcal {S}$ such that u is symmetric with respect to e and it is strictly monotone in the angular variable in a sector of angle θ/2. The result applies to least-energy and nodal least-energy solutions in spaces of functions invariant by rotations and produces multiplicity results.

Symmetry and monotonicity results for solutions of semilinear PDEs in sector-like domains

“…In [12,Proposition 1.4] it has been proved that for any k = 1, 2, … , there exists an exponent p k > 1 such that the least energy solution of the Lane-Emden problem in the space of H 1 functions that are 2 k periodic in is nonradial when p > p k . Moreover, by [13], up to a rotation, these solutions are strictly monotone in in the sector Ω 0…”